Hi,
The answer to this is probably straightforward, I have a dataframe and I'd
like to build an index of column combinations, e.g.
col1 col2 --> col3 (the index I need)
A 1 1
A 1 1
A 2 2
B 1 3
B 2 4
B 2 4
At the moment I use:
col3 <- apply(mat[,sel.col], 1, paste0)
But I wonder if another approach could be faster?
Thanks,
Emmanuel
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